Combine flour, baking powder, and salt. Stir well to blend.
In a large bowl, cream shortening, white sugar, eggs, and vanilla together; beat until light and fluffy. Add flour mixture to creamed mixture alternately with milk, making 3 dry and 2 liquid additions; combine lightly after each. Spread batter evenly into 2 greased and floured 8 inch round layer cake pans.
Bake at 350 degrees F (175 degrees C) for 35 to 40 minutes, or until toothpick inserted in center comes out clean. Cool cake in pan 10 minutes, then turn out on wire rack to cool completely.
Cream butter or margarine. Gradually blend in confectioners' sugar, cream, and lemon juice. Beat until light and creamy. Fill and frost the cake. Decorate top with a ring of well drained mandarin orange segments around outside edge. Fill center with well drained crushed pineapple. Decorate center with a few additional orange sections.